1. Technical Field
The present invention relates to a multi-cylinder internal combustion engine having at least one cylinder row with an intake side and an exhaust side. The intake side has an intake manifold, and the exhaust side has at least one exhaust manifold common to a group of cylinders. There is at least one charging unit that is connected at its pressure side to in intake air line opening into the intake manifold. There is also an arrangement for exhaust gas recirculation from the exhaust side of the engine to its intake side.
2. Background
Exhaust gas recirculation, what is known as EGR, is a generally known method in which a part of the total exhaust gas flow of the engine is returned and this part flow is introduced on the inlet side of the engine, where it is mixed with incoming air, to be introduced into the cylinders of the engine. In this way, it is possible to reduce the quantity of nitrogen oxide in the exhaust gases. Although this technique has been in use for a relatively long time, there are a number of problem areas that require solutions.
For example, it can be difficult to produce a sufficient quantity of EGR, in view of engine type and speed/loading. It is also desirable for the transfer of EGR from the exhaust side to the intake side to take place with as little effect as possible on the pressure ratio of the engine (ratio between the pressure on the inlet side and the exhaust side). From the point of view of installation, it is desirable to avoid long and hot pipe runs in the engine, especially on account of inlet and exhaust ducts having outlets on different sides of the cylinder head of the engine. Transfer of EGR can normally take place only when the pressure on the exhaust side of the engine is higher than the pressure on the intake side.
In most cases, one or more EGR valves with a shut-off function are required in order to regulate the quantity of EGR. In order to bring about rapidity of regulation, the EGR valves should be located as close to the exhaust side (the source) as possible, so that the duct volume, between ordinary exhaust valves and a turbo unit connected to the engine, is changed as little as possible by the fitting of the EGR system on the engine. EGR valves are therefore often located close to the exhaust manifold of the engine. However, such positioning is not advantageous from the point of view of service life, as a moving function must be maintained in a very hot environment. In order to cope with the heat, cool ant (or air, for example) is often required, but in some cases lubrication in the form of oil is also necessary, which complicates the construction. If the EGR valve is located on the colder intake side of the engine, it can be designed more simply, but it is then difficult to avoid an increased duct volume upstream of the EGR valve. In diesel-engine-driven trucks with an exhaust-pressure-regulated engine brake, high exhaust pressures are obtained, which the EGR cooler also has to withstand.
One object of the present invention is to produce an internal combustion engine with exhaust gas recirculation, and that is adapted to make it possible to design the EGR system more simply and more correctly, with short duct lengths and with a possibility for cooling the EGR valves.
To this end, an internal combustion engine configured according to the invention is characterized in that the arrangement for exhaust gas recirculation from the exhaust side of the engine to its intake side includes a recirculation passage arranged in the cylinder head(s) of the engine. The respective group of cylinders forms a connection between the exhaust manifold and the intake side, and can be opened and closed by a valve means. By virtue of this design of the cylinder head, exhaust gases can be transported from the exhaust side to the intake side via a very short extra passage.
In an advantageous illustrative embodiment of the invention, the valve means can be regulated by control means in such a manner that the passage is opened when the pressure in the associated exhaust manifold is higher than the pressure in the intake manifold, under such circumstances when exhaust gases are to be recirculated.
The valve means are suitably located in the cylinder head(s) of the engine. In this connection, the valve means can be cooled by means of the ordinary cooling system and oil/oil mist and/or coolant of the cylinder head, that is to say no extra pipe connections or the like are required.
According to a further advantageous illustrative embodiment of the invention, the means for exhaust gas recirculation includes a cooler, typically known as an ECR cooler, for cooling the recirculated gas.
The control means can suitably be acted on for moderation of the pressure difference between the exhaust side and the intake side and thus the engine braking effect during engine braking by means of an exhaust gas pressure regulator connected to the engine.
In this connection, the EGR valve can be used as a complement to an exhaust brake arrangement.